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Q1— Section header —
1.2A six pole DC motor has a lap connected arma ture with 800 conductors. The brushes are displaced through six mechanical degrees from
1.2.1emagnetising and cross magnetising ampere turns per pole (7\
1.2.2dditional field current required to neutralise this demagnetisation if the field winding has 1 340 turns per pole (2\
1.3A 120 V DC shunt motor takes an armature current of 58 A at a speed of 750 r/min, the flux per pole being 0, 05 wb and the armature circuit resistance 0,23 ohms. Determine each of the following i f the flux
1.3.1alue to which the armature current will increase
1.3.2peed to which the motor wil l accelerate gnore inductive effects and armature reaction and assume that the load torque remains constant. (2
Q2— Section header —
2.1A circuit has a resistance of 8 ohms, an inductance of 0,6 henry and a variable capacitance which are c onnected in series across a 125 V 50 Hz supply. Calculate each of the following:
2.1.1apacitance to give resonance (4\
2.1.2oltage across the resistance, the inductance and the capacitance (3\ 8080085
2.2A coil takes a current of 10 A and dissipates 2 100 W when connected to a 240 V 50 Hz sinusoidal supply. When another coil i s connected in parallel with it the total current taken from the same supply is 26 A at a power factor of
2.2.1otal current (11\
2.2.2ower factor (2\ [20]20
Q3— Section header —
3.2Give THREE methods of reducing a leak age flux in a transformer. (3\
3.3A 135 kVA single phase transformer has a transformation ratio of 4: 1. The primary and secondary resistances are 0,2 ohms and 0,03 ohms respectively and the corresponding leakage reactances are 1,4 ohms and 0,045 ohm
3.3.1econdary terminal voltage at full load if the power factor is 0,86 lagging (9\
3.3.2Reactance per unit (2\
3.3.3Resistance per unit (2\ .3.4 Impedance per unit (2\ [20]20
Q4— Section header —
4.1The power input to a 2 200 three phase delta connected induction motor is 82 kW and the power factor of the motor is 0,899 lagging.
4.1.1hase current (3
4.1.2kVA rating of the motor (1\ 8080085 Copyright reserved
4.2A three phase overhead line of 10 km long has solid copper conductors with diameter of 0,8 cm. Calculate the inductance and capacitance if the lines are
4.2.140 cm between adjacent centres in flat regular spacing
4.2.2n the corners of a triangle having sides of length 40 cm, 70 cm and 100 cm (2 5\ (10\
4.3The two wattmeter method is a pplied to a three phase, three wire
Q5— Section header —
5.1ame TWO methods used to find the slip of an inductio n motor. (2 5.
5.3A three phase slip ring induction motor with a star connected rotor has an induced
5.3.1otor current per pha se when the motor is running at 4% slip (5\
5.3.2er centage slip and rotor current per phase when the mot or is developing maximum torque (6\ [20] TOTAL:20